The invention relates to a method and device for cutting off a thick-walled pipe. In this description a thick-walled pipe refers to a pipe with a wall thickness of approximately 10 to 50 mm. The outer diameters of such pipes may vary between 80 and 400 mm, for instance.
According to the prior art, a pipe is cut off by a single-blade saw. In single-blade cutting, the diameter of the blade should be larger than the diameter of the pipe to be cut. Also, the thickness of the blade with a large diameter is great and the structure of the saw is sufficiently firm to use the blade with a large diameter. A greater thickness of the blade causes material losses. Furthermore, it is expensive to acquire big blades.
Patent publication GB 884591 A discloses a solution with two cutting blades, wherein a pipe is sawn towards the centre with two saws to accelerate the cutting procedure. In this solution, as the blades approach each other, one of the blades is withdrawn and the other one finishes the cutting procedure. In this solution, blade costs are doubled because both blades should have at least the size of the pipe diameter. In addition, such a saw with two big blades has a power demand that is considerably greater than that of the saw mentioned previously.
In both prior art solutions, during one blade revolution the blade comes into contact with the pipe wall twice after passing through the pipe wall. If a thick-walled pipe is cut off, a problem arises that a sizable chip removed from the first wall will not necessarily be detached from the throat of the blade before it touches the wall a second time during the same blade revolution. This makes the cutting less effective and may result in breaking of the blade.